This invention concerns a mechanism for presenting weft threads on weaving machines. The mechanism is intended primarily to present weft threads to the grippers of rapier weaving machines.
As is known, several aspects are involved in presenting a weft thread to a gripper. First it is important, in order to obtain smooth operation, when a thread has to be presented twice or several times in succession, that the thread presentation arm should not carry out a to and fro motion, but should remain in its presented position. A weaving machine which applies this principle is known from U.S. Pat. No. 3,092,150.
On rapier weaving machines it is also important that the motion of the thread presentation arm from the presented position to the rest position should be carried out as late as possible, in order for the weft thread not to come in contact with the upper warp sheet. Also, presentation of a weft thread must begin soon enough in order to bring the weft thread into the path of the gripper in good time. Otherwise, if the weft thread is presented too soon, it may come in contact with the weft thread inserted previously, so that the weft threads may be damaged or become entangled.
Normally the optimum conditions are achieved when a presentation arm being activated and a presentation arm being deactivated cross each other at about the moment that the last weft thread to have been inserted is being beaten up. At that moment, the weft threads attached to the respective presentation arms have a more or less common starting point, namely the end of the fell line on the picking side. The threads cannot get crossed then, so there is no chance of entanglement.
On known mechanisms, the presentation arm of the thread to be presented on the one hand and the presentation arm of a thread which has just been presented and inserted into the shed on the other are moved simultaneously over the same period. Since the time over which this period extends is very restricted because of the above-mentioned requirements, the thread presentation arms have to make a very quick, brusque movement, which has disadvantages in terms of the forces involved, wear, noise etc.